Since the development of lasers, optical heterodyne conversion (photomixing) has been useful for coherent detection in many regions of the electromagnetic spectrum. Photomixing has also been proposed as a technique for generating coherent radiation in the microwave and millimeter-wave regions, and interest in this technique has been revived recently by the advances in high-speed III-V device technology. Of the two applications, coherent generation has been much less useful than coherent detection because of the lack of a suitable photomixer. Although difference frequencies have been generated up to 61 GHz, the generated power has been severely limited by at least one of several factors such as low photomixer bandwidth, poor optical power coupling, impedance mismatch between the photomixer element and the load circuit, and degradation of the photomixer properties at high optical pump power.